Heat and pressure consolidated laminates are generally produced utilizing a core material comprising a plurality of phenolic resin impregnated paper sheets, a decor sheet impregnated with a melamine-formaldehyde resin and, optionally, a melamine-formaldehyde resin impregnated overlay sheet. These laminates have found world-wide success as construction materials i.e. wall panels, countertops etc., in the home and office. They can be prepared so as to function in a variety of service applications and can be produced with surfaces of high gloss, a matte finish or an embossed finish. They can be rendered post-formable with the application of heat and can be cut or worked much in the same manner as other building materials.
Although the above-described laminates have found a high degree of success over the past forty years, there is a continual need to improve the laminates and/or the method of their preparation and, accordingly, research is always on the outlook for means to achieve such improvements.
Two of the properties of heat and pressure consolidated laminates for which an ongoing search for improvement is continually being conducted are the post-formability and the dark edge line present in all laminates containing cores produced from phenolic resins. That is to say, post-forming ability is now imparted to decorative, heat and pressure consolidated laminates by using a combination of X-creped papers and a less than fully cured resin system in the core. The X-creped papers are substituted in part or in full for the kraft papers which are normally used in non-postforming laminates and, in the production of the laminates per se, the cure cycle employed in the laminating press is such that the resin components in the laminates are not fully cured. The under-curing of the resins reduces the laminate rigidity and enables post-forming to be effected with the application of additional heat in the area of the desired bend.
The dark edge line that is perceptable when conventional laminates are cut or worked has been a particularly difficult problem. If the resin impregnated into the core sheets is a phenolic resin, a photo-darkening takes place upon such exposure resulting in the undesirable edge line. If a water-clear melamine/formaldehyde resin is used to replace the conventional phenolic resin, even if modified with known cross-linking suppressants, laminates made therefrom do not meet the required NEMA Standard properties for high pressure decorative laminate and also often discolor upon exposure, although to a lesser degree than phenolics.
Accordingly, a long-felt need would be satisfied if the post-formability and/or dark edge line of decorative laminates could be improved.